This invention relates generally to composition and process for treating combustion gases to remove the noxious sulfur dioxide. More particularly, the present invention relates to process and composition for reducing the emission of SO.sub.2 from the flue gas obtained during the combustion of sulfur-containing coal.
It is very evident in recent years that the shortage of energy sources is rapidly becoming critical. Gaseous and liquid fuels have in recent years become the principal source of energy for both industrial and private uses. Coal, the more commonly used energy source, prior to the advent of greater reliance upon the gaseous and liquid fuels has fallen into some disfavor principally due to the common presence of sulfur often in high percentages (i.e. greater than 2% by weight). When combusted, coal containing sulfur produces sulfur dioxide which if present in sufficient quantities does not meet government standards for clean air.
To avoid air pollution problems, greater commerical use has been made of the gaseous and liquid fuels while much of the great mass of coal remains unused. The shortage of gaseous and liquid fuels however has rekindled a burning interest in the use of coal as a major, if not principal, source of energy. Coal with low content of sulfur (less than 2% by weight) is actively being in order to meet the legal standards for clean air but sufficient low sulfur coal is not readily available. It is ironic that areas of the United States known to have massive deposits of coal such as Appalachia in fact must import low sulfur coal from other regions to meet the government standards because the Appalachia coal often has a high sulfur content in the range over 2% sulfur.
The advent of new reliance upon coal as a major energy source has produced a great variance in the price of coal depending upon the sulfur content. The low sulfur content coal which may be burned and produces combustion gas within the clean air requirements is approximately 1.5 to 2% by weight sulfur. This coal, not being readily available where it might be used, is considerably more expensive than the coal of approximately 3% sulfur and greater sulfur content. Quite naturally the high sulfur coal is quite inexpensive but more significantly it is readily available in huge quantities to meet the energy demands for many years to come. It is known, for instance, that prior treatments of the stack gas have been attempted but even those using a liquid additive have been found unsuccessful due to the production of a residue that must be removed or additionally treated.
To date, effective and economic means of removing sulfur from coal prior to its combustion have not been found to be practical and therefore if the high sulfur coal is to be used without polluting the air the SO.sub.2 produced must be removed or at least reduced to acceptable standards.